# Quantitative Chemical Analysis 7e_1_

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Quantitative Chemical
Analysis
ACCURATE   ACCURATE       NOT Accurate
PRECISE    NOT precise    PRECISE

Random error   systematic error
Required math skills:
•   Subtract
•   Multiply
•   Divide
•   Powers
•   Logarithms
•   Orders of magnitude
•   Estimation
•   Units
•   Conversions
•   Powers of 10
•   Prefixes
•   Errors
•   Statistics
Estimation and orders of magnitude:

How many piano
tuners are there in
Chicago?
Estimation and orders of magnitude:

What is the
national debt?
Estimation and orders of magnitude:

What is the world
population?
Estimation and orders of magnitude:

How many water
molecules in 1000
droplets?
Estimation and orders of magnitude:

A cube – 1” on a side  (2.6)3 cm3 ~ 18 cc

1g
18 cc = 18 cc       18 g
1 cc
N molecules
18 g = 18 g                6.022 x 1023 molecules
18 g
Estimation and orders of magnitude: powers of 10
Chemical concentrations

Molarity = Moles of solute/Liters of Solution (M)

Molality = Moles of solute/Kg of Solvent (m)

Mole Fraction = Moles solute/total number of moles

Mass % = Mass solute/total mass x 100

Volume % = volume solute/total volume x 100

ppm = parts per million *
ppb = parts per billion *

* mass for solutions, volume for gasses
Chemical concentrations

Molarity = Moles of solute/Liters of Solution (M)

Molality = Moles of solute/Kg of Solvent (m)

Mole Fraction = Moles solute/total number of moles

Mass % = Mass solute/total mass x 100

Volume % = volume solute/total volume x 100

ppm = parts per million *
ppb = parts per billion *

* mass for solutions, volume for gasses
Chemical concentrations

Molarity = Moles of solute/Liters of Solution (M)

Molality = Moles of solute/Kg of Solvent (m)

Mole Fraction = Moles solute/total number of moles

Mass % = Mass solute/total mass x 100

Volume % = volume solute/total volume x 100

ppm = parts per million *
ppb = parts per billion *

* mass for solutions, volume for gasses
A sample of NaNO3 weighing 8.50 grams is placed in a 500. ml
volumetric flask and distilled water was added to the mark on the
neck of the flask. Calculate the Molarity of the resulting
solution.
A sample of NaNO3 weighing 8.50 grams is placed in a 500. ml
volumetric flask and distilled water was added to the mark on the
neck of the flask. Calculate the Molarity of the resulting
solution.

1. Convert the given grams of solute to moles of solute :
1 mole NaNO3
8.50 g NaNO3                   0.100 mole NaNO3
85 g NaNO3
2. Convert given ml of solution to liters

1 liter
500. ml           0.500 liter
1000 ml
3. Apply the definition for Molarity:
Molarity = moles NaNO3 / volume of the solution in liters

0.100 mole
Concentration               0.100 M
0.500 liter
Chemical concentrations

Molarity = Moles of solute/Liters of Solution (M)

Molality = Moles of solute/Kg of Solvent (m)

Mole Fraction = Moles solute/total number of moles

Mass % = Mass solute/total mass x 100

Volume % = volume solute/total volume x 100

ppm = parts per million *
ppb = parts per billion *

* mass for solutions, volume for gasses
Determine the molality of 3000. grams of solution containing 37.3 grams of
Potassium Chloride KCl.

1. Convert grams KCl to moles KCl

1 mole KCl
37.3 g KCl                   0.500 mole KCl
74.6 g KCl

2. Determine the mass of pure solvent from the given grams of solution and
solute
Determine the molality of 3000. grams of solution containing 37.3 grams of
Potassium Chloride KCl.

1. Convert grams KCl to moles KCl

1 mole KCl
37.3 g KCl                   0.500 mole KCl
74.6 g KCl

2. Determine the mass of pure solvent from the given grams of solution and
solute

Total grams = 3000 grams = Mass of solute + Mass of solvent
 Mass of pure solvent = (3000 - 37.3) gram
= 2962.7 gram
.

3. Convert grams of solvent to kilograms

1 kg
2962.7 grams solvent                   2.9627 kg
1000 grams
4. Apply the definition for molality

0.500 moles
concentration               0.169 m
2.9627 kg
Chemical concentrations

Molarity = Moles of solute/Liters of Solution (M)

Molality = Moles of solute/Kg of Solvent (m)

Mole Fraction = Moles solute/total number of moles

Mass % = Mass solute/total mass x 100

Volume % = volume solute/total volume x 100

ppm = parts per million *
ppb = parts per billion *

* mass for solutions, volume for gasses
Determine the mole fraction of KCl in 3000. grams of solution containing
37.3 grams of Potassium Chloride KCl.

1. Convert grams KCl to moles KCl

1 mole KCl
37.3 g KCl                   0.500 mole KCl
74.6 g KCl

2. Determine the mass of pure solvent from the given grams of solution and
solute
Determine the molality of 3000. grams of solution containing 37.3 grams of
Potassium Chloride KCl.

1. Convert grams KCl to moles KCl

1 mole KCl
37.3 g KCl                   0.500 mole KCl
74.6 g KCl

2. Determine the mass of pure solvent from the given grams of solution and
solute

Total grams = 3000 grams = Mass of solute + Mass of solvent
 Mass of pure solvent = (3000 - 37.3) gram
= 2962.7 gram
3. Convert grams of solvent H2O to mols

1 mol
2962.7 grams water                      164.6 mols H 2O
18.0 grams

4. Apply the definition for mole fraction mole fraction =

moles of KCl                   0.5100
               =0.00303
total moles of KCl + water         0.500  164.6
Chemical concentrations

Molarity = Moles of solute/Liters of Solution (M)

Molality = Moles of solute/Kg of Solvent (m)

Mole Fraction = Moles solute/total number of moles

Mass % = Mass solute/total mass x 100

Volume % = volume solute/total volume x 100

ppm = parts per million *
ppb = parts per billion *

* mass for solutions, volume for gasses
Determine the mass % of a NaCl solution if 58.5 grams of NaCl was dissolved in 50
ml of water (assume the density of water to be 1 g/ml)

1. Convert ml of water to grams

1g
 50 ml          50 grams water
1 ml
2. Determine total mass of solution

Mass of solution = mass of solute + mass of solvent =
58.5 + 50 = 108.5 g

3. Apply the definition of mass percent mass % =

58.5 (100) / 108.5 = 53.9% NaCl
Chemical concentrations

Molarity = Moles of solute/Liters of Solution (M)

Molality = Moles of solute/Kg of Solvent (m)

Mole Fraction = Moles solute/total number of moles

Mass % = Mass solute/total mass x 100

Volume % = volume solute/total volume x 100

ppm = parts per million *
ppb = parts per billion *

* mass for solutions, volume for gasses
Assuming the density of water to be 1 g/mL we approximate the
density of a dilute aqueous solution to be 1 g/mL

1 g
1 ppm =
1g
1 g 1 g 1 g
         
1 g 1 ml 1 ml

 1 ppm = 1 μg/mL = 1 mg/L

 1 ppb = 1 ng/mL = 1 μg/L
Determine the ppm of a NaCl solution if 58.5 grams of NaCl was dissolved in 50.0
ml of water (assume the density of water to be 1 g/ml)

Convert ml of water to grams

1g
 50 ml          50 grams water
1 ml
Determine total mass of solution

Mass of solution = mass of solute + mass of solvent =
58.5 + 50.0 = 108.5 g

Apply the definition of ppm

58.5 (106) / 108.5 = 5.39 x 105 ppm NaCl

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 views: 3 posted: 2/1/2012 language: pages: 39